Etching a substrate: processes – Etching to produce porous or perforated article
Patent
1994-06-09
1996-02-13
Powell, William
Etching a substrate: processes
Etching to produce porous or perforated article
216 95, 156148, 156155, 428137, B31D 300, B44C 122
Patent
active
054906024
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method of manufacturing composite structures and is particularly although not exclusively concerned with the manufacture of a filament reinforced perforate composite sheet for use as a facing sheet of a structural component usually referred to as an acoustic liner and used for acoustic attenuation in high level noise aircraft environments such as those in aircraft engine nacelles.
Various facing sheets have been proposed for aircraft acoustic liners. From a noise attenuation view point the so called "linear" liners are currently the most successful. Improved facing sheets for these "linear" liners have been proposed and include for example (i) a stainless steel mesh bonded to an inner perforate aluminium sheet, (ii) a stainless steel mesh bonded to an inner open-weave advanced composite sheet and (iii) a microporous thermoplastic sheet bonded to an open weave advanced composite sheet. Prior to the introduction of the above mentioned linear liner facing sheets, perforate aluminium alloy facing sheets were used.
There is however still a need for a simple perforate facing sheet where for example the increased noise attenuation properties of the linear liners are not required, as in small inherently quiet engines. Also linear liners with the improved facing sheets can be more expensive to produce and/or heavier than those using simple perforate facing sheets.
When a linear with a simple perforate facing sheet is all that is required the ideal choice from a weight saving and fatigue view point is an advanced composite perforate structure eg, carbon/epoxy, carbon/bismaleimide, kevlar/epoxy or the like. Although there is a wide range of manufacturing options for these structures all have disadvantages in one form or another including the following: results in mechanical damage and the capital expenditure required to produce such a large number of holes is very high. limitations; the moulds are very complex and expensive; and release from the moulds over such a large number of holes and from a complex three dimensioned shape presents a problem in production. roughness; hole geometry (especially maintaining tight open area tolerances) and resin content problems give rise to poor mechanical and acoustical performance.
It is an object of the present invention to provide a method of manufacturing a filament reinforced perforate composite sheet which does not suffer from or does not suffer to the same extent from the above-mentioned disadvantages found in the previously proposed methods of manufacture.
According to a first aspect of the present invention there is provided a method of manufacturing a filament reinforced perforate composite sheet comprising the steps of forming a filament assembly which includes reinforcing filament structures and passage forming filament structures and in which the passage forming filament structures extend from the front face of the assembly to the rear face of the assembly, applying a matrix material to the assembly to form a composite sheet in which the passage forming filament structures extend from the front face of the sheet to the rear face of the sheet and removing the passage forming filament structures or a predetermined part or parts thereof thereby to produce a multiplicity of passages extending through the composite sheet from the front face of the sheet to the rear face of the sheet.
The passage forming filament structures in the above mentioned embodiments of the invention may be continuous monofilaments, an assembly of continuous filaments in the form of a tow or twisted together or a yarn spun from short fibers.
In an embodiment of the invention hereinafter to be described the passage forming filament structures or a predetermined part or parts thereof are made from a selected material so selected as to transform into a dischargeable state when the sheet is subjected to a predetermined condition which does not adversely affect the material or materials from which the matrix and the other filament structures are made and the selected ma
REFERENCES:
patent: 2623241 (1952-12-01), Mackay et al.
patent: 3966522 (1976-06-01), Hatch et al.
patent: 4090002 (1978-05-01), Rosenblum
patent: 4743496 (1988-05-01), Wrasidlo et al.
patent: 4885973 (1989-02-01), Spain
Braniff Mark A.
Wilson Robert S.
Powell William
Short Brothers PLC
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